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<span class="sans">XDEBUG EXTENSION FOR PHP | DOCUMENTATION - PROTOCOL - DBGP</span><br />

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<h1 class="title">DBGP - A common debugger protocol for languages and debugger UI communication</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Version:</th>
<td>1.0</td></tr>
<tr><th class="docinfo-name">Status:</th>
<td>draft 17</td></tr>
<tr><th class="docinfo-name">Authors:</th>
<td>Shane Caraveo, ActiveState &lt;<a class="reference external" href="mailto:shanec&#64;ActiveState.com">shanec&#64;ActiveState.com</a>&gt;
<br />Derick Rethans &lt;<a class="reference external" href="mailto:derick&#64;derickrethans.nl">derick&#64;derickrethans.nl</a>&gt;</td></tr>
</tbody>
</table>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#description" id="id11">1. Description</a></li>
<li><a class="reference internal" href="#issues" id="id12">1.1 Issues</a></li>
<li><a class="reference internal" href="#requirements" id="id13">2. Requirements</a></li>
<li><a class="reference internal" href="#terminology" id="id14">3. Terminology</a></li>
<li><a class="reference internal" href="#security" id="id15">4. Security</a></li>
<li><a class="reference internal" href="#initiating-a-debugging-session" id="id16">5. Initiating a debugging session</a><ul>
<li><a class="reference internal" href="#standard-dbgp-port" id="id17">5.1 Standard DBGP port</a></li>
<li><a class="reference internal" href="#connection-initialization" id="id18">5.2 Connection Initialization</a></li>
<li><a class="reference internal" href="#just-in-time-debugging-and-debugger-proxies" id="id19">5.3 Just in time debugging and debugger proxies</a><ul>
<li><a class="reference internal" href="#init-packet-handling" id="id20">5.3.1 Init Packet Handling</a></li>
<li><a class="reference internal" href="#proxy-errors" id="id21">5.3.2 Proxy Errors</a></li>
<li><a class="reference internal" href="#proxy-ports" id="id22">5.3.3 Proxy Ports</a></li>
</ul>
</li>
<li><a class="reference internal" href="#multiple-processes-or-threads" id="id23">5.4 Multiple Processes or Threads</a></li>
<li><a class="reference internal" href="#feature-negotiation" id="id24">5.5 Feature Negotiation</a><ul>
<li><a class="reference internal" href="#data-packet-negotiation" id="id25">Data packet negotiation</a></li>
<li><a class="reference internal" href="#asynchronous-communications" id="id26">Asynchronous Communications</a></li>
</ul>
</li>
</ul>
</li>
<li><a class="reference internal" href="#message-packets" id="id27">6. Message Packets</a><ul>
<li><a class="reference internal" href="#why-not-xml-both-ways" id="id28">6.1 Why not XML both ways?</a></li>
<li><a class="reference internal" href="#packet-communications" id="id29">6.2 Packet Communications</a></li>
<li><a class="reference internal" href="#ide-to-debugger-engine-communications" id="id30">6.3 IDE to debugger engine communications</a></li>
<li><a class="reference internal" href="#debugger-engine-to-ide-communications" id="id31">6.4 debugger engine to IDE communications</a></li>
<li><a class="reference internal" href="#debugger-engine-errors" id="id32">6.5 debugger engine errors</a></li>
<li><a class="reference internal" href="#error-codes" id="id33">6.5.1 Error Codes</a></li>
<li><a class="reference internal" href="#file-paths" id="id34">6.6 file paths</a></li>
<li><a class="reference internal" href="#dynamic-code-and-virtual-files" id="id35">6.7 Dynamic code and virtual files</a></li>
</ul>
</li>
<li><a class="reference internal" href="#core-commands" id="id36">7. Core Commands</a><ul>
<li><a class="reference internal" href="#status" id="id37">7.1 status</a></li>
<li><a class="reference internal" href="#options-and-configuration" id="id38">7.2 Options and Configuration</a><ul>
<li><a class="reference internal" href="#feature-names" id="id39">7.2.1 Feature Names</a></li>
<li><a class="reference internal" href="#feature-get" id="id40">7.2.2 feature_get</a></li>
<li><a class="reference internal" href="#feature-set" id="id41">7.2.3 feature_set</a></li>
</ul>
</li>
<li><a class="reference internal" href="#continuation-commands" id="id42">7.5 continuation commands</a></li>
<li><a class="reference internal" href="#breakpoints" id="id43">7.6 breakpoints</a><ul>
<li><a class="reference internal" href="#id1" id="id44">7.6.1 breakpoint_set</a></li>
<li><a class="reference internal" href="#id2" id="id45">7.6.2 breakpoint_get</a></li>
<li><a class="reference internal" href="#id3" id="id46">7.6.3 breakpoint_update</a></li>
<li><a class="reference internal" href="#id4" id="id47">7.6.4 breakpoint_remove</a></li>
<li><a class="reference internal" href="#id5" id="id48">7.6.5 breakpoint_list</a></li>
</ul>
</li>
<li><a class="reference internal" href="#stack-depth" id="id49">7.7 stack_depth</a></li>
<li><a class="reference internal" href="#stack-get" id="id50">7.8 stack_get</a></li>
<li><a class="reference internal" href="#context-names" id="id51">7.9 context_names</a></li>
<li><a class="reference internal" href="#context-get" id="id52">7.10 context_get</a></li>
<li><a class="reference internal" href="#properties-variables-and-values" id="id53">7.11 Properties, variables and values</a></li>
<li><a class="reference internal" href="#data-types" id="id54">7.12 Data Types</a><ul>
<li><a class="reference internal" href="#common-data-types" id="id55">7.12.1 Common Data Types</a></li>
<li><a class="reference internal" href="#typemap-get" id="id56">7.12.2 typemap_get</a></li>
</ul>
</li>
<li><a class="reference internal" href="#property-get-property-set-property-value" id="id57">7.13 property_get, property_set, property_value</a></li>
<li><a class="reference internal" href="#source" id="id58">7.14 source</a></li>
<li><a class="reference internal" href="#stdout-stderr" id="id59">7.15 stdout, stderr</a></li>
</ul>
</li>
<li><a class="reference internal" href="#extended-commands" id="id60">8. Extended Commands</a><ul>
<li><a class="reference internal" href="#stdin" id="id61">8.1 stdin</a></li>
<li><a class="reference internal" href="#break" id="id62">8.2 break</a></li>
<li><a class="reference internal" href="#eval" id="id63">8.3 eval</a><ul>
<li><a class="reference internal" href="#expr" id="id64">8.3.1 expr</a></li>
<li><a class="reference internal" href="#exec" id="id65">8.3.2 exec</a></li>
</ul>
</li>
<li><a class="reference internal" href="#spawnpoints" id="id66">8.4 spawnpoints</a><ul>
<li><a class="reference internal" href="#id6" id="id67">8.4.1 spawnpoint_set</a></li>
<li><a class="reference internal" href="#id7" id="id68">8.4.2 spawnpoint_get</a></li>
<li><a class="reference internal" href="#id8" id="id69">8.4.3 spawnpoint_update</a></li>
<li><a class="reference internal" href="#id9" id="id70">8.4.4 spawnpoint_remove</a></li>
<li><a class="reference internal" href="#id10" id="id71">8.4.5 spawnpoint_list</a></li>
</ul>
</li>
<li><a class="reference internal" href="#notifications" id="id72">8.5 Notifications</a><ul>
<li><a class="reference internal" href="#standard-notifications" id="id73">8.5.1 Standard Notifications</a></li>
</ul>
</li>
<li><a class="reference internal" href="#interact-interactive-shell" id="id74">8.6 interact - Interactive Shell</a></li>
</ul>
</li>
<li><a class="reference internal" href="#a-changelog" id="id75">A. ChangeLog</a></li>
</ul>
</div>
<div class="section" id="description">
<h1><a class="toc-backref" href="#id11">1. Description</a></h1>
<p>This document describes a simple protocol for use with language tools
and engines for the purpose of debugging applications.  It does not
describe user interfaces or interactions with the debugger.  The
protocol provides a means of communication between a debugger
engine (scripting engine, vm, etc.) and a debugger IDE (IDE, etc.).
Any references to the debugger IDE UI are recommendations only, and are
provided for additional explanation or as reasoning for specific
design decisions.</p>
</div>
<div class="section" id="issues">
<h1><a class="toc-backref" href="#id12">1.1 Issues</a></h1>
<p>1. The handling of proxy errors needs to be clarified.  Without both
IDE and debugger engine supporting commands to be received at
arbitrary times, the proxy may have problems sending error or status
information to either one.  See section 5.3.2.  We should think a bit
more about what a proxy might need to do.</p>
</div>
<div class="section" id="requirements">
<h1><a class="toc-backref" href="#id13">2. Requirements</a></h1>
<ul class="simple">
<li>extensibility, allow for vendor or language specific features</li>
<li>backwards and forwards compatibility</li>
<li>firewall and tunneling support</li>
<li>support for multiple languages</li>
<li>support for multiple processes or threads</li>
<li>support for dynamic and possibly for compiled languages</li>
</ul>
</div>
<div class="section" id="terminology">
<h1><a class="toc-backref" href="#id14">3. Terminology</a></h1>
<dl class="docutils">
<dt>IDE</dt>
<dd>An IDE, or other debugger UI IDE or tool.</dd>
<dt>debugger engine</dt>
<dd>The language engine being debugged.</dd>
<dt>proxy</dt>
<dd>An intermediary demon that acts as a proxy, and may also
implement support for other features such as just in time
debugging, ip security, etc.</dd>
<dt>session</dt>
<dd>a single thread in an application.  multiple threads in an
application will attach separately.</dd>
<dt>TRUE</dt>
<dd>a value defined as TRUE should be a numeric one.</dd>
<dt>FALSE</dt>
<dd>a value defined as FALSE should be a numeric zero.</dd>
<dt>NUM</dt>
<dd>a base 10 numeric value that is stringified.</dd>
</dl>
</div>
<div class="section" id="security">
<h1><a class="toc-backref" href="#id15">4. Security</a></h1>
<p>It is expected that implementations will provide security, such as ip
filtering, ssh tunneling, etc.  This protocol itself does not provide
a means of securing the debugging session.</p>
</div>
<div class="section" id="initiating-a-debugging-session">
<h1><a class="toc-backref" href="#id16">5. Initiating a debugging session</a></h1>
<p>The debugger engine initiates a debugging session.  The debugger engine
will make a connection to a listening IDE, then wait for the IDE to
initiate commands.  The debugger engine does not step into the first line of
execution until the IDE issues one of the continuation commands.
The first thing that should happen in a debug session is that the IDE
negotiates features using the feature_get and feature_set commands, and sets
any additional data, such as breakpoints.  Debugger engine implementations
should store and data it receives if it is unable to process them prior to
compiling and/or executing code.  Commands such as stack_get should not be
expected to work during this phase, otherwise known as the 'starting' state (see
section 7.1 for status levels).</p>
<p>Likewise, at the end of a debug session, there is a 'stopping' state.  This state
is entered after all execution is complete.  For most debugger engine implementations,
only a 'stop' command can be accepted at this point, however some implementations
may provide additional commands for retrieving various data from the engine for
post debug session processing.</p>
<div class="section" id="standard-dbgp-port">
<h2><a class="toc-backref" href="#id17">5.1 Standard DBGP port</a></h2>
<p>The IDE listens on port 9000 for debugger connections, unless the
IDE is using a proxy, in which case it may listen on any port.  In
that case, the IDE will tell the proxy which port it is listening on, and the
proxy should listen on port 9000.  While this document defines port 9000
as the standard DBGP port, an implementation may support the use of any
port.  Current implementations accept various forms of configuration that
allow this port to be defined.</p>
</div>
<div class="section" id="connection-initialization">
<h2><a class="toc-backref" href="#id18">5.2 Connection Initialization</a></h2>
<p>When a debugger engine connects to either a IDE or proxy, it must send an
init packet:</p>
<pre class="literal-block">
&lt;init appid=&quot;APPID&quot;
      idekey=&quot;IDE_KEY&quot;
      session=&quot;DBGP_COOKIE&quot;
      thread=&quot;THREAD_ID&quot;
      parent=&quot;PARENT_APPID&quot;
      language=&quot;LANGUAGE_NAME&quot;
      protocol_version=&quot;1.0&quot;
      fileuri=&quot;file://path/to/file&quot;&gt;
</pre>
<p>Attributes in the init element can include:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="22%" />
<col width="78%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Attribute</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>appid</td>
<td>defined by the debugger engine</td>
</tr>
<tr><td>idekey</td>
<td>defined by the user.  The DBGP_IDEKEY environment
variable SHOULD be used if it is available,
otherwise setting this value is debugger engine
implementation specific.  This value may be empty.</td>
</tr>
<tr><td>session</td>
<td>If the environment variable DBGP_COOKIE exists,
then the init packet MUST contain a session
attribute with the value of the variable.  This
allows an IDE to execute a debugger engine, and
maintain some state information between the
execution and the protocol connection.  This value
should not be expected to be set in 'remote'
debugging situations where the IDE is not in
control of the process.</td>
</tr>
<tr><td>thread</td>
<td>the systems thread id</td>
</tr>
<tr><td>parent</td>
<td>the appid of the application that spawned the
process.  When an application is executed, it
should set it's APPID into the environment.
If an APPID already exists, it should first
read that value and use it as the PARENT_APPID.</td>
</tr>
<tr><td>language</td>
<td>debugger engine specific, must not contain
additional information, such as version, etc.</td>
</tr>
<tr><td>protocol_version</td>
<td>The highest version of this protocol supported</td>
</tr>
<tr><td>fileuri</td>
<td>URI of the script file being debugged</td>
</tr>
</tbody>
</table>
</blockquote>
<p>The IDE responds by dropping socket connection, or starting with
debugger commands.</p>
<p>The init packet may have child elements for additional vendor specific
data.  These are entirely optional and must not effect behavior
of the debugger interaction.  Suggested child elements include:</p>
<pre class="literal-block">
&lt;engine version=&quot;1.abcd&quot;&gt;product title&lt;/engine&gt;
&lt;author&gt;author&lt;/author&gt;
&lt;company&gt;company&lt;/company&gt;
&lt;license&gt;licensing info&lt;/license&gt;
&lt;url&gt;url&lt;/url&gt;
&lt;copyright&gt;xxx&lt;/copyright&gt;
</pre>
</div>
<div class="section" id="just-in-time-debugging-and-debugger-proxies">
<h2><a class="toc-backref" href="#id19">5.3 Just in time debugging and debugger proxies</a></h2>
<p>Proxies are supported to allow multiuser systems work with a defined
port for debugging.  Each IDE would listen on a unique port and notify the
proxy what port it is listening on, along with a key value that is used by
the debugger engine to specify which IDE it should be connected with.</p>
<p>With the exception of the init packet, all communications
will be passed through without modifications.  A proxy could also implement
support for just in time debugging.  In this case, a debugger engine would
break (perhaps on an error or exception) and connect to the proxy.  The proxy
would then start the IDE (if it is not already running) and initiate a
debugging session with it.</p>
<p>The method for handling just in time debugging is not defined by the protocol
and is implementation specific.  One example of how this may work is that the
proxy has a configuration file that defines key's for each user, along with
the path to the executable that will provide the UI for that user.  The debugger
engine would have to know this key value in advance and provide it to the proxy
in the init packet (see IDE_KEY in section 5.2).  The proxy would know if the
IDE is running, since the IDE should have communicated with the proxy already,
if it has not, the proxy could execute the IDE directly.</p>
<p>To support proxies and jit deamons, the IDE should be configured with
and ip:port pointing to the proxy/jit.  The IDE then makes a
connection to the proxy when it starts and sends the following command:</p>
<blockquote>
<p>IDE command</p>
<pre class="literal-block">
proxyinit -a ip:port -k ide_key -m [0|1]
</pre>
<table border="1" class="docutils">
<colgroup>
<col width="3%" />
<col width="97%" />
</colgroup>
<tbody valign="top">
<tr><td>-p</td>
<td>the port that the IDE listens for debugging on.  The address
is retrieved from the connection information.</td>
</tr>
<tr><td>-k</td>
<td>a IDE key, which the debugger engine will also use in it's
debugging init command.  this allows the proxy to match
request to IDE.  Typically the user will provide the
session key as a configuration item.</td>
</tr>
<tr><td>-m</td>
<td>this tells the demon that the IDE supports (or doesn't)
multiple debugger sessions.  if -m is missing, zero or no
support is default.</td>
</tr>
</tbody>
</table>
<p>IDE command</p>
<pre class="literal-block">
proxystop -k ide_key
</pre>
<p>The IDE sends a proxystop command when it wants the proxy
server to stop listening for it.</p>
</blockquote>
<p>The proxy should respond with a simple XML statement alerting the
IDE to an error, or the success of the initialization (see section
6.5 for more details on the error element).</p>
<pre class="literal-block">
&lt;proxyinit success=&quot;[0|1]&quot;
           idekey=&quot;{ID}&quot;
           address=&quot;{IP_ADDRESS}&quot;
           port=&quot;{NUM}&gt;
    &lt;error id=&quot;app_specific_error_code&quot;&gt;
        &lt;message&gt;UI Usable Message&lt;/message&gt;
    &lt;/error&gt;
&lt;/proxyinit&gt;
</pre>
<p>Once the IDE has sent this command, and received a confirmation, it
disconnects from the proxy.  The IDE will only connect to the proxy
when it initially wants to start accepting connections from the proxy,
or when it wants to stop accepting connections from the proxy.</p>
<p>The address and port attributes of the returned proxyinit element are the
address and port that the proxy is configured to listen for DBGP connections on.
This information is returned to the IDE so that it may pass this information on
to build systems or the user via some UI.</p>
<div class="section" id="init-packet-handling">
<h3><a class="toc-backref" href="#id20">5.3.1 Init Packet Handling</a></h3>
<p>If a proxy receives the init packet (see section 5.2), it will use the
idekey attribute to pass the request to the correct IDE, or to do some
other operation such as which may be required to implement security or
initiate just in time debugging.  The proxy will add the idekey as a attribute
to the init packet when it passes it through to the IDE.  The proxy may
also add child elements with further information, and must add an
attribute to the init element called 'proxied' with the attribute
value being the ip address of the debugger engine.  This is the only
time the proxy should modify data being passed to the IDE.</p>
</div>
<div class="section" id="proxy-errors">
<h3><a class="toc-backref" href="#id21">5.3.2 Proxy Errors</a></h3>
<p>If the proxy must send error data to the IDE, it may send an XML
message with the root element named 'proxyerror'.  This message will
be in the format of the error packets defined in 6.3 below.</p>
<p>If the proxy must send error data to the debugger engine, it may
send the proxyerror command defined in section 7 below.</p>
</div>
<div class="section" id="proxy-ports">
<h3><a class="toc-backref" href="#id22">5.3.3 Proxy Ports</a></h3>
<p>The proxy listens for IDE connections on port 9001, and for debugger
engine connections on port 9000.  As with section 5.1, these ports may
be configurable in the implementation.</p>
</div>
</div>
<div class="section" id="multiple-processes-or-threads">
<h2><a class="toc-backref" href="#id23">5.4 Multiple Processes or Threads</a></h2>
<p>The debugger protocol is designed to use a separate socket connection
for each process or thread.  The IDE may or may not support
multiple debugger sessions.  If it does not, the debugger engine must
not attempt to start debug sessions for threads, and the IDE should
not accept more than one socket connection for debugging.  The
IDE should tell the debugger engine whether it supports multiple
debugger sessions, the debugger engine should assume that the IDE does
not.  The IDE can use the feature_set command with the feature name of
'multiple_sessions' to notify the debugger engine that it supports multiple
session debugging.  The IDE may also query the the debugger engine specifically
for multithreaded debugging support by using the feature_get command with
a feature name of 'language_supports_threads'.</p>
</div>
<div class="section" id="feature-negotiation">
<h2><a class="toc-backref" href="#id24">5.5 Feature Negotiation</a></h2>
<p>Although the IDE may at any time during the debugging session send
feature_get or feature_set commands, the IDE should be designed to
negotiate the base set of features up front.  Differing languages and
debugger engines may operate in many ways, and the IDE should be
prepared to handle these differences.  Likewise, the IDE may dictate
certain features or capabilities be supported by the debugger engine.
In any case, the IDE should strive to work with all debugger engines
that support this protocol.  Therefore, this section describes a
minimal set of features the debugger engine must support.  These
required features are outlined here in the form of discussion,
actual implementation of feature arguments are detailed in section 7
under the feature_get and feature_set commands.</p>
<div class="section" id="data-packet-negotiation">
<h3><a class="toc-backref" href="#id25">Data packet negotiation</a></h3>
<p>IDE's may want to limit the size of data that is retrieved from
debugger engines.  While the debugger engines will define their own
base default values, the IDE should negotiate these terms if it
needs to.  The debugger engine must support these requests from the
IDE.  This includes limits to the data size of a property or
variable, and the depth limit to arrays, hashes, objects, or other
tree like structures.  The data size excludes any the protocol
overhead.</p>
</div>
<div class="section" id="asynchronous-communications">
<h3><a class="toc-backref" href="#id26">Asynchronous Communications</a></h3>
<p>While the protocol does not depend on asynchronous socket support,
certain design considerations may require that the IDE and/or debugger
engine treat incoming and outgoing data in an asynchronous fashion.</p>
<p>For ease of design, some implementations may choose to utilize this
protocol in a completely synchronous fashion, and not implement
optional commands that require the debugger engine to behave in an
asynchronous fashion.  One example of this is the break command.</p>
<p>The break command is sent from the IDE while the debugger engine is
in a run state.  To support this, the debugger engine must periodically
peek at the socket to see if there are any incoming commands.  For
this reason the break command is optional.  If a command requires
this type of asynchronous behavior on the part of the debugger
engine it must be optional for the debugger engine to support it.</p>
<p>On the other hand, IDE's MUST at times behave in an asynchronous
fashion.  When an IDE tells the debugger engine to enter a 'run' state,
it must watch the socket for incoming packets for stdout or stderr,
if it has requested the data be sent to it from the debugger engine.</p>
<p>The form of asynchronous communications that may occur in this
protocol are defined further in section 6.2 below.</p>
</div>
</div>
</div>
<div class="section" id="message-packets">
<h1><a class="toc-backref" href="#id27">6. Message Packets</a></h1>
<p>The IDE sends simple ASCII commands to the debugger engine.  The
debugger engine responds with XML data.  The XML data is prepended
with a stringified integer representing the number of bytes in the XML data
packet.  The length and XML data are separated by a NULL byte.  The
XML data is ended with a NULL byte.  Neither the IDE or debugger engine
packets may contain NULL bytes within the packet since it is used as
a separator.  Data must be encoded using base64.</p>
<pre class="literal-block">
IDE:       command [SPACE] [args] -- data [NULL]
DEBUGGER:  [NUMBER] [NULL] XML(data) [NULL]
</pre>
<p>Arguments to the IDE commands are in the same format as common command
line arguments, and should be parseable by common code such as getopt,
or Pythons Cmd module:</p>
<pre class="literal-block">
command -a value -b value ...
</pre>
<p>If a value for an option includes a space, the value needs to be
encoded. You can encode values by encasing them in double quotes:</p>
<pre class="literal-block">
property_get -i 5 -n &quot;$x['a b']&quot; -d 0 -c 0 -p 0
</pre>
<p>It is also possible to use escape characters in quoted strings:</p>
<pre class="literal-block">
property_get -i 6 -n &quot;$x[\&quot;a b\&quot;]&quot; -d 0 -c 0 -p 0
</pre>
<p>All numbers in the protocol are base 10 string representations, unless
the number is noted to be debugger engine specific (eg. the address
attribute on property elements).</p>
<div class="section" id="why-not-xml-both-ways">
<h2><a class="toc-backref" href="#id28">6.1 Why not XML both ways?</a></h2>
<p>The primary reason is to avoid the requirement that a debugger
engine has an XML parser available.  XML is easy to generate, but
requires additional libraries for parsing.</p>
</div>
<div class="section" id="packet-communications">
<h2><a class="toc-backref" href="#id29">6.2 Packet Communications</a></h2>
<p>The IDE sends a command, then waits for a response from the
debugger engine.  If the command is not received in a reasonable
time (implementation dependent) it may assume the debugger engine
has entered a non-responsive state.  The exception to this is when
the IDE sends a 'continuation' command which may not have an immediate response.</p>
<p>'continuation' commands include, but may not be limited to: run, step_into,
step_over, step_out and eval.  When the debugger engine
receives such a command, it is considered to have entered a
'run state'.</p>
<p>During a 'continuation' command, the IDE should expect to possibly receive
stdin and/or stderr packets from the debugger engine prior to
receiving a response to the command itself.  It may also possibly
receive error packets from either the debugger engine, or a proxy
if one is in use, either prior to the 'continuation' response, or in response
to any other command.</p>
<p>Stdout and stderr, if requested by the IDE, may only be sent during
commands that have put the debugger engine into a 'run' state.</p>
<p>If the debugger engine supports asynchronous commands, the IDE may also
send commands while the debugger engine is in a 'run' state.  These
commands should be limited to commands such as the 'break' or 'status'
commands for performance reasons, but this protocol does not impose
such limitations.  The debugger engine MUST respond to these commands
prior to responding to the original 'run' command.</p>
<p>An example of communication between IDE and debugger engines.  (this
is not an example of the actual protocol.)</p>
<pre class="literal-block">
IDE:  feature_get supports_async
DBG:  yes
IDE:  stdin redirect
DBG:  ok
IDE:  stderr redirect
DBG:  ok
IDE:  run
DBG:  stdin data...
DBG:  stdin data...
DBG:  reached breakpoint, done running
IDE:  give me some variables
DBG:  ok, here they are
IDE:  evaluate this expression
DBG:  stderr data...
DBG:  ok, done
IDE:  run
IDE:  break
DBG:  ok, breaking
DBG:  at breakpoint, done running
IDE:  stop
DBG:  good bye
</pre>
</div>
<div class="section" id="ide-to-debugger-engine-communications">
<h2><a class="toc-backref" href="#id30">6.3 IDE to debugger engine communications</a></h2>
<p>A debugging IDE (IDE) sends commands to the debugger engine in
the form of command line arguments.  One argument that is included in
all commands is the data length.  The data itself is the last part of
the command line, after the -- separator.  The data must be base64 encoded.</p>
<pre class="literal-block">
command [SPACE] [arguments] [SPACE] -- base64(data) [NULL]
</pre>
<p>Standard arguments for all commands</p>
<pre class="literal-block">
-i      Transaction ID
        unique numerical ID for each command generated by the IDE
</pre>
</div>
<div class="section" id="debugger-engine-to-ide-communications">
<h2><a class="toc-backref" href="#id31">6.4 debugger engine to IDE communications</a></h2>
<p>The debugger engine always replies or sends XML data.  The standard
namespace for the root elements returned from the debugger
engine MUST be &quot;<a class="reference external" href="urn:debugger_protocol_v1">urn:debugger_protocol_v1</a>&quot;.  Namespaces have been left
out in the examples in this document.  The messages sent by the
debugger engine must always be NULL terminated.  The XML document tag
must always be present to provide XML version and encoding information.</p>
<p>Two base tags are used for the root tags:</p>
<pre class="literal-block">
data_length
[NULL]
&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;
&lt;response command=&quot;command_name&quot;
          transaction_id=&quot;transaction_id&quot;/&gt;
[NULL]

data_length
[NULL]
&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;
&lt;stream type=&quot;stdout|stderr&quot;&gt;...Base64 Data...&lt;/stream&gt;
[NULL]
</pre>
<p>For simplification, data length and NULL bytes will be left out of the
rest of the examples in this document.</p>
</div>
<div class="section" id="debugger-engine-errors">
<h2><a class="toc-backref" href="#id32">6.5 debugger engine errors</a></h2>
<p>A debugger engine may need to relay error information back to the IDE in
response to any command.  The debugger engine may add an error element
as a child of the response element.  Note that this is not the same
as getting language error messages, such as exception data.  This is
specifically a debugger engine error in response to a IDE
command.  IDEs and debugger engines may elect to support additional
child elements in the error element, but should namespace the elements
to avoid conflicts with other implementations.</p>
<pre class="literal-block">
&lt;response command=&quot;command_name&quot;
          transaction_id=&quot;transaction_id&quot;&gt;
    &lt;error code=&quot;error_code&quot; apperr=&quot;app_specific_error_code&quot;&gt;
        &lt;message&gt;UI Usable Message&lt;/message&gt;
    &lt;/error&gt;
&lt;/response&gt;
</pre>
</div>
<div class="section" id="error-codes">
<h2><a class="toc-backref" href="#id33">6.5.1 Error Codes</a></h2>
<p>The following are predefined error codes for the response to commands:</p>
<p>000 Command parsing errors</p>
<pre class="literal-block">
0 - no error
1 - parse error in command
2 - duplicate arguments in command
3 - invalid options (ie, missing a required option, invalid value for a
    passed option)
4 - Unimplemented command
5 - Command not available (Is used for async commands. For instance
    if the engine is in state &quot;run&quot; then only &quot;break&quot; and &quot;status&quot;
    are available).
</pre>
<p>100 File related errors</p>
<pre class="literal-block">
100 - can not open file (as a reply to a &quot;source&quot; command if the
      requested source file can't be opened)
101 - stream redirect failed
</pre>
<p>200 Breakpoint, or code flow errors</p>
<pre class="literal-block">
200 - breakpoint could not be set (for some reason the breakpoint
      could not be set due to problems registering it)
201 - breakpoint type not supported (for example I don't support
      'watch' yet and thus return this error)
202 - invalid breakpoint (the IDE tried to set a breakpoint on a
      line that does not exist in the file (ie &quot;line 0&quot; or lines
      past the end of the file)
203 - no code on breakpoint line (the IDE tried to set a breakpoint
      on a line which does not have any executable code. The
      debugger engine is NOT required to return this type if it
      is impossible to determine if there is code on a given
      location. (For example, in the PHP debugger backend this
      will only be returned in some special cases where the current
      scope falls into the scope of the breakpoint to be set)).
204 - Invalid breakpoint state (using an unsupported breakpoint state
      was attempted)
205 - No such breakpoint (used in breakpoint_get etc. to show that
      there is no breakpoint with the given ID)
206 - Error evaluating code (use from eval() (or perhaps
      property_get for a full name get))
207 - Invalid expression (the expression used for a non-eval()
      was invalid)
</pre>
<p>300 Data errors</p>
<pre class="literal-block">
300 - Can not get property (when the requested property to get did
      not exist, this is NOT used for an existing but uninitialized
      property, which just gets the type &quot;uninitialised&quot; (See:
      PreferredTypeNames)).
301 - Stack depth invalid (the -d stack depth parameter did not
      exist (ie, there were less stack elements than the number
      requested) or the parameter was &lt; 0)
302 - Context invalid (an non existing context was requested)
</pre>
<p>900 Protocol errors</p>
<pre class="literal-block">
900 - Encoding not supported
998 - An internal exception in the debugger occurred
999 - Unknown error
</pre>
</div>
<div class="section" id="file-paths">
<h2><a class="toc-backref" href="#id34">6.6 file paths</a></h2>
<p>All file paths passed between the IDE and debugger engine must be in
the URI format specified by IETF RFC 1738 and 2396, and must be
absolute paths.</p>
</div>
<div class="section" id="dynamic-code-and-virtual-files">
<h2><a class="toc-backref" href="#id35">6.7 Dynamic code and virtual files</a></h2>
<p>The protocol reserves the URI scheme 'dbgp' for all virtual
files generated and maintained by language engines. Such
virtual files are usually managed by a language engine for
dynamic code blocks, i.e. code created at runtime, without
an association with a regular file. Any IDE seeing an URI
with the 'dbgp' scheme has to use the 'source' command (See
section 7.14) to obtain the contents of the file from the
engine responsible for that URI.</p>
<p>All URIs in that scheme have the form:</p>
<blockquote>
dbgp:engine-specific-identifier</blockquote>
<p>The engine-specific-identifier is some string which the debugger engine
uses to keep track of the specific virtual file.  The IDE must return
the URI to the debugger engine unchanged through the source command to
retrieve the virtual file.</p>
</div>
</div>
<div class="section" id="core-commands">
<h1><a class="toc-backref" href="#id36">7. Core Commands</a></h1>
<p>Both IDE and debugger engine must support all core commands.</p>
<div class="section" id="status">
<h2><a class="toc-backref" href="#id37">7.1 status</a></h2>
<p>The status command is a simple way for the IDE to find out from
the debugger engine whether execution may be continued or not.
no body is required on request.  If async support has been
negotiated using feature_get/set the status command may be sent
while the debugger engine is in a 'run state'.</p>
<p>The status attribute values of the response may be:</p>
<blockquote>
<dl class="docutils">
<dt>starting:</dt>
<dd>State prior to execution of any code</dd>
<dt>stopping:</dt>
<dd>State after completion of code execution.  This typically
happens at the end of code execution, allowing the IDE to
further interact with the debugger engine (for example, to
collect performance data, or use other extended commands).</dd>
<dt>stopped:</dt>
<dd>IDE is detached from process, no further interaction is
possible.</dd>
<dt>running:</dt>
<dd>code is currently executing.  Note that this
state would only be seen with async support
turned on, otherwise the typical state during
IDE/debugger interaction would be 'break'</dd>
<dt>break:</dt>
<dd>code execution is paused, for whatever reason
(see below), and the IDE/debugger can pass
information back and forth.</dd>
</dl>
</blockquote>
<p>The reason attribute value may be:</p>
<blockquote>
<ul class="simple">
<li>ok</li>
<li>error</li>
<li>aborted</li>
<li>exception</li>
</ul>
</blockquote>
<p>IDE</p>
<pre class="literal-block">
status -i transaction_id
</pre>
<p>debugger engine</p>
<pre class="literal-block">
&lt;response command=&quot;status&quot;
          status=&quot;starting&quot;
          reason=&quot;ok&quot;
          transaction_id=&quot;transaction_id&quot;&gt;
    message data
&lt;/response&gt;
</pre>
</div>
<div class="section" id="options-and-configuration">
<h2><a class="toc-backref" href="#id38">7.2 Options and Configuration</a></h2>
<p>The feature commands are used to request feature support from the debugger
engine. This includes configuration options, some of which may be changed via
feature_set, the ability to discover support for implemented commands, and to
discover values for various features, such as the language version or name.</p>
<p>An example of usage would be to send a feature request with the string 'stdin'
to find out if the engine supports redirection of the stdin stream through the
debugger socket. The debugger engine must consider all commands as keys for this
command, but may also have keys that are for features that do not map directly
to commands.</p>
<div class="section" id="feature-names">
<h3><a class="toc-backref" href="#id39">7.2.1 Feature Names</a></h3>
<p>The following features strings MUST be available:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="34%" />
<col width="9%" />
<col width="57%" />
</colgroup>
<tbody valign="top">
<tr><td>language_supports_threads</td>
<td>get</td>
<td>[0|1]</td>
</tr>
<tr><td>language_name</td>
<td>get</td>
<td>{eg. PHP, Python, Perl}</td>
</tr>
<tr><td>language_version</td>
<td>get</td>
<td>{version string}</td>
</tr>
<tr><td>encoding</td>
<td>get</td>
<td>current encoding in use by the debugger
session. The encoding can either be
(7-bit) ASCII, or a code set which
contains ASCII (Ex: ISO-8859-X, UTF-8)</td>
</tr>
<tr><td>protocol_version</td>
<td>get</td>
<td>{for now, always 1}</td>
</tr>
<tr><td>supports_async</td>
<td>get</td>
<td>{for commands such as break}</td>
</tr>
<tr><td>data_encoding</td>
<td>get</td>
<td>optional, allows to turn off
the default base64 encoding of data. This
should only be used for development and
debugging of the debugger engines
themselves, and not for general use. If
implemented the value 'base64' must be
supported to turn back on regular
encoding. the value 'none' means no
encoding is in use. all elements that use
encoding must include an encoding
attribute.</td>
</tr>
<tr><td>breakpoint_languages</td>
<td>get</td>
<td>some engines may support more than one
language. This feature returns a string
which is a comma separated list of
supported languages. <strong>If the engine does
not provide this feature, then it is
assumed that the engine only supports the
language defined in the feature
language_name.</strong> One example of this is an
XSLT debugger engine which supports XSLT,
XML, HTML and XHTML. An IDE may need this
information to to know what types of
breakpoints an engine will accept.</td>
</tr>
<tr><td>breakpoint_types</td>
<td>get</td>
<td>returns a space separated list with all
the breakpoint types that are supported.
See <a class="reference internal" href="#breakpoints">7.6 breakpoints</a> for a list of the
6 defined breakpoint types.</td>
</tr>
<tr><td>multiple_sessions</td>
<td>get|set</td>
<td>{0|1}</td>
</tr>
<tr><td>encoding</td>
<td>get|set</td>
<td>{ISO8859-15, UTF-8, etc.}</td>
</tr>
<tr><td>max_children</td>
<td>get|set</td>
<td>max number of array or object
children to initially retrieve</td>
</tr>
<tr><td>max_data</td>
<td>get|set
get|set</td>
<td>max amount of variable data to
initially retrieve.</td>
</tr>
<tr><td>max_depth</td>
<td>get|set</td>
<td>maximum depth that the debugger
engine may return when sending arrays,
hashs or object structures to the IDE.</td>
</tr>
</tbody>
</table>
</blockquote>
<p>The following features strings MAY be available, if they are not, the IDE should
assume that the feature is not available:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="34%" />
<col width="9%" />
<col width="57%" />
</colgroup>
<tbody valign="top">
<tr><td>supports_postmortem</td>
<td>get</td>
<td>[0|1]  This feature lets an IDE know that
there is benefit to continuing interaction
during the STOPPING state (sect. 7.1).</td>
</tr>
<tr><td>show_hidden</td>
<td>get|set</td>
<td>[0|1]  This feature can get set by the IDE
if it wants to have more detailed internal
information on properties (eg. private
members of classes, etc.)  Zero means that
hidden members are not shown to the IDE.</td>
</tr>
<tr><td>notify_ok</td>
<td>get|set</td>
<td>[0|1]  See section 8.5</td>
</tr>
</tbody>
</table>
</blockquote>
<p>Additionally, all protocol commands supported must have a string,
such as the following examples:</p>
<pre class="literal-block">
breakpoint_set
break
eval
</pre>
</div>
<div class="section" id="feature-get">
<h3><a class="toc-backref" href="#id40">7.2.2 feature_get</a></h3>
<p>arguments for feature_get include:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="5%" />
<col width="95%" />
</colgroup>
<tbody valign="top">
<tr><td>-n</td>
<td>feature_name</td>
</tr>
</tbody>
</table>
</blockquote>
<p>IDE</p>
<pre class="literal-block">
feature-get -i transaction_id -n feature_name
</pre>
<p>debugger engine</p>
<pre class="literal-block">
&lt;response command=&quot;feature_get&quot;
          feature_name=&quot;feature_name&quot;
          supported=&quot;0|1&quot;
          transaction_id=&quot;transaction_id&quot;&gt;
    feature setting or available options, such as a list of
    supported encodings
&lt;/response&gt;
</pre>
<p>The 'supported' attribute does NOT mean that the feature is supported, this
is encoded in the text child of the response tag. The 'supported' attribute
informs whether the feature with 'feature_name' is supported by feature_get
in the engine, or when the command with name 'feature_get' is supported by the
engine.</p>
<p>Example: Xdebug does not understand the 'breakpoint_languages' feature
and will therefore set the supported attribute to '0'. It does however
understand the feature 'language_supports_threads' and the 'supported'
attribute is therefore set to '1', but as PHP does not support threads,
the returned value is in this case &quot;0&quot;.</p>
</div>
<div class="section" id="feature-set">
<h3><a class="toc-backref" href="#id41">7.2.3 feature_set</a></h3>
<p>The feature set command allows a IDE to tell the debugger engine what additional
capabilities it has. One example of this would be telling the debugger engine
whether the IDE supports multiple debugger sessions (for threads, etc.). The
debugger engine responds with telling the IDE whether it has enabled the feature
or not.</p>
<p>Note: The IDE does not have to listen for additional debugger connections if it
does not support debugging multiple sessions. debugger engines must handle
connection failures gracefully.</p>
<p>arguments for feature_set include:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="5%" />
<col width="95%" />
</colgroup>
<tbody valign="top">
<tr><td>-n</td>
<td>feature_name</td>
</tr>
<tr><td>-v</td>
<td>value to be set</td>
</tr>
</tbody>
</table>
</blockquote>
<p>feature_set can be called at any time during a debug session to
change values previously set.  This allows a IDE to change
encodings.</p>
<p>IDE</p>
<pre class="literal-block">
feature_set -i transaction_id -n feature-name -v value
</pre>
<p>debugger engine</p>
<pre class="literal-block">
&lt;response command=&quot;feature_set&quot;
          feature=&quot;feature_name&quot;
          success=&quot;0|1&quot;
          transaction_id=&quot;transaction_id&quot;/&gt;
</pre>
</div>
</div>
<div class="section" id="continuation-commands">
<h2><a class="toc-backref" href="#id42">7.5 continuation commands</a></h2>
<p>resume the execution of the application.</p>
<dl class="docutils">
<dt>run:</dt>
<dd>starts or resumes the script until a new breakpoint is reached,
or the end of the script is reached.</dd>
<dt>step_into:</dt>
<dd>steps to the next statement, if there is a function call
involved it will break on the first statement in that function</dd>
<dt>step_over:</dt>
<dd>steps to the next statement, if there is a function call on the
line from which the step_over is issued then the debugger engine
will stop at the statement after the function call in the same
scope as from where the command was issued</dd>
<dt>step_out:</dt>
<dd>steps out of the current scope and breaks on the statement after
returning from the current function. (Also called 'finish' in
GDB)</dd>
<dt>stop:</dt>
<dd>ends execution of the script immediately, the debugger engine may
not respond, though if possible should be designed to do so.
The script will be terminated right away and be followed by a
disconnection of the network connection from the IDE (and debugger
engine if required in multi request apache processes).</dd>
<dt>detach (optional):</dt>
<dd>stops interaction with the debugger engine.  Once this command
is executed, the IDE will no longer be able to communicate with
the debugger engine.  This does not end execution of the script
as does the stop command above, but rather detaches from debugging.
Support of this continuation command is optional, and the IDE should
verify support for it via the feature_get command.  If the IDE has
created stdin/stdout/stderr pipes for execution of the script
(eg. an interactive shell or other console to catch script output),
it should keep those open and usable by the process until the process
has terminated normally.</dd>
</dl>
<p>The response to a continue command is a status response (see
status above).  The debugger engine does not send this response
immediately, but rather when it reaches a breakpoint, or ends
execution for any other reason.</p>
<p>IDE</p>
<pre class="literal-block">
run -i transaction_id
</pre>
<p>debugger engine</p>
<pre class="literal-block">
&lt;response command=&quot;run&quot;
          status=&quot;starting&quot;
          reason=&quot;ok&quot;
          transaction_id=&quot;transaction_id&quot;/&gt;
</pre>
</div>
<div class="section" id="breakpoints">
<h2><a class="toc-backref" href="#id43">7.6 breakpoints</a></h2>
<p>Breakpoints are locations or conditions at which a debugger engine
pauses execution, responds to the IDE, and waits for further commands
from the IDE.  A failure in any breakpoint commands results in an
error defined in <a class="reference internal" href="#debugger-engine-errors">section 6.5</a>.</p>
<p>The following DBGP commands relate to breakpoints:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="27%" />
<col width="73%" />
</colgroup>
<tbody valign="top">
<tr><td><a class="reference internal" href="#id1">breakpoint_set</a></td>
<td>Set a new breakpoint on the session.</td>
</tr>
<tr><td><a class="reference internal" href="#id2">breakpoint_get</a></td>
<td>Get breakpoint info for the given breakpoint id.</td>
</tr>
<tr><td><a class="reference internal" href="#id3">breakpoint_update</a></td>
<td>Update one or more attributes of a breakpoint.</td>
</tr>
<tr><td><a class="reference internal" href="#id4">breakpoint_remove</a></td>
<td>Remove the given breakpoint on the session.</td>
</tr>
<tr><td><a class="reference internal" href="#id5">breakpoint_list</a></td>
<td>Get a list of all of the session's breakpoints.</td>
</tr>
</tbody>
</table>
</blockquote>
<p>There are six different breakpoints <em>types</em>:</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="21%" />
<col width="17%" />
<col width="62%" />
</colgroup>
<thead valign="bottom">
<tr><th class="head">Type</th>
<th class="head">Req'd Attrs</th>
<th class="head">Description</th>
</tr>
</thead>
<tbody valign="top">
<tr><td>line</td>
<td>filename,
lineno</td>
<td>break on the given lineno in the given
file</td>
</tr>
<tr><td>call</td>
<td>function</td>
<td>break on entry into new stack for
function name</td>
</tr>
<tr><td>return</td>
<td>function</td>
<td>break on exit from stack for function
name</td>
</tr>
<tr><td>exception</td>
<td>exception</td>
<td>break on exception of the given name</td>
</tr>
<tr><td>conditional</td>
<td>expression,
filename</td>
<td>break when the given expression is true
at the given filename and line number or
just in given filename</td>
</tr>
<tr><td>watch</td>
<td>expression</td>
<td>break on write of the variable or address
defined by the expression argument</td>
</tr>
</tbody>
</table>
</blockquote>
<p>A breakpoint has the following attributes. Note that some attributes are only
applicable for some breakpoint types.</p>
<blockquote>
<table border="1" class="docutils">
<colgroup>
<col width="24%" />
<col width="76%" />
</colgroup>
<tbody valign="top">
<tr><td>type</td>
<td>breakpoint type (see table above for valid types)</td>
</tr>
<tr><td>filename</td>
<td>The file the breakpoint is effective in. This must be
a &quot;<a class="reference external" href="file://">file://</a>&quot; or &quot;dbgp:&quot; (See <a class="reference internal" href="#dynamic-code-and-virtual-files">6.7 Dynamic code and
virtual files</a>) URI.</td>
</tr>
<tr><td>lineno</td>
<td>Line number on which breakpoint is effective…